to that, of iluoresccin. The simplest of these 'compounds is
represented by the following formula :—
1}R Kl'A RATION 83.
reaction" for the preparation of hydroxyaldehydes from phenols
is applicable to a very lar^'e number of monohydric and-poly-
hydric phenols. The substitution of two II atoms by two alde-
hyde groups sometimes occurs, as in the case of resorcinol. An
analogous reaction is that of caustic potash and carbon tetra*
chloride on phenol, which yields chiefly /»-hydroxybenxoic acid,
(',11,011 ! CCI., I SKOII ~ (.Y.HI-'' -I- 4KC1 -!• 3ILO.
Salicylic Acid. —The reaction was discovered by Kolbe,
and is known as tl Kolbc's synthesis." It will have been ob-
served that it takes place in t\vo steps. Sodium phenylcarbdnate
is iirst formed, which then undergoes intramolecular change
•with the production of sodium salicylate (Schmidt). The tech-
nical process is carried out in autoclaves, in which carbon
dioxide is passed into the sodium phenate under pressure at
1 20 130'. It is a curious fact that the use of potassium phenate
yields, especially at a hiyh temperature (220' ), almost exclusively
the /<>»hydroxybeim>ate of potassium.
The above reaction may be applied in the case of other
I'RKPA RATION 85.
Quinone and Quinol. Ouinone, which was originally
obtained by the oxidation of quinic acid (the acid associated